Diffusion transistor



April 4, 1961 H. DoRENDoRF DIFFUSION TRANSISTOR Original Filed July l0, 1957 megacycles.

United i States Patent f 2,978,617v y j DIFFUSION TRANSISTOR a Iclaims priority, application `Germany July 2s, 1956 i 519 claims. (ci. 3115235) 'l This application Yis a diyisionof copending application Serial No. 671,062, filed July 10, 1957, now Patent No. 2,945,286, dated July 19, 1960, and the invention disclosed herein relates to transistors and is particularly concerned with a diffusion transistor.

In diffusion transistors, some zones of dilfering conduction type are generally formed very thin. In known structures, these zones are preferably produced by dilusion of donors and acceptors from a gaseous phase.

N-p-n transistors, made preferably of silicon, have been proposed especially for operating at high frequencies, the contacting of the p-conducting base being effected through the emitter by means of an aluminum wire which does not act in a blocking sense, or only slightly in a blocking sense, relative to the n-conducting emitter layer arranged thereabove and perforated thereby. This mode of operation is applied, for example, in using silicon as a semiconductor, aluminum and antimony acting as majority carriers. A corresponding semiconductor arrangement may for ,example be used up to a frequency of 100 In case germanium is used as a serniconductor material, a known arrangement will be found advantageous, comprising a p-conducting germanium basic crystal carrying an n-layer produced thereon by diffusion and contacted by a relatively wide gold-antimony electrode. Immediately adjacent thereto there is a layer of aluminum vaporized on the crystal, such layer acting as a p-layer.

It has also been proposed to provide for contacting in the case of high frequency transistors having a very thin -base zone, to cut the semiconductor crystal forming an n-p-nv layer, at a small angle to the plane of the layer limit, thereby producing a relatively wide cutting surface along the base. It is, however, generally quite difficult to iind exactly the limits containing the p-layer to be contacted and to provide the corresponding area with a contact.

The object of the invention is to effect the contacting of the base in a ditfusion transistor in simple manner, without having to carry the electrode through a zone of .other conduction type in order to obtain satisfactory blocking characteristics.

This object is according to the invention realized, in

A semiconductor according to the invention exhibits a l stepped configuration, each step being formed by a zone of different conduction type. Adjacent a relatively thick, extended n-region of the base crystal, there is provided a thin and less extensive p-zone and on the latter is disposed a still smaller n-zone.l The thick n-zone as well as the thin n-zoneare upon their Vfree surfaces provided with a solder, for example, tin, for low resistance contacting of vthe electrode terminals.

Further details of the invention will/appear from the description of an embodiment which is rendered below with reference to the accompanying drawing.y

The drawing shows in the lower part a relatively thick n-layer 3, formed, for example, by an n-germanium semiconductor crystal, serving as collector. On top lof this crystal is disposed a p-layer 4, serving as a base,l carrying in turn a smaller nlayer.5 which operates as emitter. To the base 4 is alloyed a wireV 6 which'may advantageously consist of gold containing about 1% gallium. 'I'he emitter layer Sis contacted with a suitable solder, for example, tin 1, which is connected with a suitable wire `7,` `for example, a copper wire. The thick n-layer The transistor according to the invention may be made,`

for example, as follows:

Along the surface of an n-conductive germanium crystal is produced, for example, by dilusion from a gaseous phase, a p-layer, and upon the latter a rfurther n-diffusion layer. The top n-layer receives a solder point with a diameter, for example, of 0.3 mm.' The solder point and a small surrounding area are masked by suitable means and the remaining surface of the crystal is etched. The etching may be carried on, for example, for intervals of tive seconds, until the n-layer along the unmasked surface is completely removed. The proper instant for the termination of the etching may be determined by testing the thermal voltage occurring between a hot point set in contact with the crystal surface, and a support for the lower n-layer.

After the top n-layer outside the masked area is etched olf, a wider surrounding area is provided with an acidproof mask, and the etching is repeated to remove in this manner the undesired portion of the p-layer serving as the base.

As indicated before, the gold wire alloyed with gallium, is thereafter contacted with the exposed p-layer, preferably alloyed thereto and the solder points, provided upon the two outer n-layers as described, are connected with electrodes.

It has been assumed that the zones in an arrangement according to the invention are zones of specific conduction type; it being understood however, that these zones may be of dilferent conduction type and/or different in purity content, and the term conduction type is accordingly intended to embrace both conditions.

Transistors according to the invention are easily produced since the base can be readily contacted, and are especially suitable for operation at high frequencies. Furthermore, very low blocking current will flow between the base and the emitter, resulting in a particularly favorable curve of the blocking characteristic which is above all important in the use of the transistor as a switch.

Transistors according to the invention may be used up to a limit frequency of about 20 megacycles.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

I claim:

1. A semiconductor arrangement for high frequency operation, comprising at least three zones with adjacent zones being of different conduction type, two mutually adjacent zones being relatively very thin as compared with the third zone, the areas occupied by said zones increasing stepwise from zone to zone in the direction of the third zone, and means for atleast partially contacting the free surface portion of at least the second zone resulting from the stepwise configuration of said zones.

2. A semiconductor arrangement according to claim l,

wherein one of said zones operates as a base'zone, com-Y prising terminal means for contacting said base zone, said terminal means consisting of gold containing gallium.

3. A semiconductor arrangement according toclaim l, wherein one of said zones operates as an n-zone, and solder means for connecting a copper electrode 10W ohmic with said n-zone.

4. A semiconductor arrangement according to claim l, forming ann-p-n diffusion transistor, wherein said three zones comprise an n-conducting semiconductor crystal forming a collector and a p-zone forming the base and an n-layer disposed upon said p-zone and forming an emitter.

5. A semiconductor arrangement according to claim 4, comprising terminal means consisting of gold containing gallium connected to Asaid base.

6. A semiconductor arrangement according to claim 4,

References `Cited inthe iileof this patent UNITED STATES PATENTS Derendorf July 19, 1960 Philips Sept. 20, 1960 Notice of Adverse Decision in Interference In Interference No. 93,330 involving Patent No. 2,978,617, H. Derendorf, Diffusion translstor, final judgment adverse to the patentee was rendered July 8,

1964:, as to claims 1, 4L and 7 [Oez'wl Gazette August 25, 1964.]

Notice of Adverse Decision in Interference In Interference No. 93,330 involving Patent No. 2,978,617, H. Derendorf, Diffusion translstor, final judgment adverse to the patentee was rendered July 8,

1964:, as to claims 1, 4L and 7 [Oez'wl Gazette August 25, 1964.]

Notice of Adverse Decision in Interference In Interference No. 98,330 involving Patent N o. 2,978,617, H. Dorendorf, Diffusion transistor, nal judgment adverse to the patentee was rendered July 8,

1964, as to claims l, 4 and 7.

[Oficial Gazette August 25, 1964.] 

